30

THE COLLIERY GUARDIAN.

January 7, 1916.

possible needs of those who purchase their greatest rival in
the nitrogen market. Thus, not only the sulphate needs of
farmers, but all British requirements in nitrogen are being
provided for before any sulphate of ammonia is being
exported, and that only under licence, to prevent its reaching
our enemies.

The returns for the week have been :—Pitch, 2,853 tons,
and T144. Tar, 21,076.galls., T82. Tar oil, 4,000 galls. to
Bergen. Sulphate of ammonia, 2,420 tons.

ANNEALING CAGE CHAINS.

In view of the fact that the General Regulations dated
July 10, 1913, made in pursuance of 'section 86 of the
Coal Mines Act, 1911, prescribe that “ all cage chains in
general use shall be annealed once at least in every six
months,” the following information on 'annealing, given
in a recently issued Home Office Memorandum on
“ Chains and Other Lifting Appliances,” by Mr. G. S.
Taylor, H.M. inspector of factories, may be of interest.

The metal of which chains and similar appliances are
constructed becomes hardened by overstrain, produced
by stresses which exceed, the elastic limit, either with
an overload, or when a load is suddenly applied or
quickly arrested during its descent. Such overstrain
alters the physical properties of the metal, -and the
alteration may continue for days or even months, with
gradual development of greater hardness, and a conse-
quent decrease in the power of elongation, changes
attributed by Unwin to the slow accumulation of per-
manent. set. A similar effect is produced in wrought
iron and mild steel by working or hammering these
metals at a ” blue heat,” i.e., between 450degs. and
600 degs. Fahr. In this hardened condition, the metal
is more liable to fracture by shock owing to absence
of local ductile yielding. The hardening effect of over-
strain is removed by the process of annealing, which
consists in healing the metal to redness (about 1,400
degs. Fahr.) and cooling it slowly. After such treat-
ment the metal reverts to its former state as regards
ductility, but is generally reduced in ultimate strength.

In addition to the hardening, the metal of a chain
undergoes deterioration due to .repeated loading, an
effect known as “ fatigue,” which is common to most-
metals used in construction. Owing to “ fatigue,” a
load considerably below the ultimate strength of n bar, if
it is removed and applied a sufficient number of times,
will eventually cause its fracture. Recent research has
shown that ‘ ‘ fatigue ’ ’ does not produce crystallisation
of the metal, nor can its effect be removed by annealing.

Cast iron links of conveyor chains are converted into
malleable cast iron by a process, wrongly called
“ annealing,” (in which the castings are placed in boxes
of powdered haematite (iron oxide) and maintained at a
red heat for several days. This treatment decarburises
the. skin of the casting and a portion of the interior,
makes the meUal malleable like wrought iron, and
increases its tenacity.

Annealing has long been recognised as a useful pre-
caution for lessening the risk of fracture in chains and
similar lifting appliances, and is largely adopted by
chain users. Methods of annealing vary, and some have
certain disadvantages, but the best is that known as
“ close annealing,” a process used by a few firms who
have (the necessary plant. The chain or article to be
•annealed is placed in a gas- or oil-fired muffle furnace,
heated to redness, while avoiding contact with the air,
and then allowed to cool slowly either in the furnace or
covered with dry sand or ashes after removal. “ Close
annealing ” prevents oxidation and subsequent scaling
of the surface of the metal, and the chain is heated more
uniformly than in other types of furnaces. Coal or coke
may also be used for a “ close annealing ” furnace, and
a fire clay gas retort is said to make a good muffle for
these furnaces.

In many works, however, annealing is done either in
an ordinary reverberatory furnace used for heating
plates, or in a small furnace of the same type specially
built for the purpose. The chain or articles should not
come into contact with the fuel, which should be as free
as possible from sulphur or phosphorus. Where an
ordinary plate. furnace is used, the chains are often
placed in the hot furnace on Saturday, and removed on
the following Monday, when quite cold. In special
annealing furnaces the chains are maintained at a uni-
form red heat for some time; after removal they are
either allowed to cool in a mass on the shop floor, or
covered with sand or ashes and cooled slowly. It is
contended by some that cooling in sand or ashes is
unnecessary for wrought iron articles containing littlle, if
any, carbon, whilst these precautions are considered
essential by others. Possibly the cooling en masse is
almost as effective for practical purposes, especially if
the articles are covered with plates to prevent the chill
ing effect of cold air. Several chain users, however,
have demonstrated by experiment the advantage of slow
cooling, and the results of tests by Mr. Frank Law, of
Careless Green, Staffordshire, show that the ductility of
iron, as indicated by the contraction of area and elonga-
tion of a fractured sample, is greater with slow cooling
than with rapid cooling, thought the ultimate strength
is reduced by the former.

One method, of annealing consists in passing a chain
link by link through an ordinary smith’s fire. Each
link is heated to redness, then .removed from the fire,
and examined carefully whilst red hot. Cracks or flaws
can then be more readily detected. The chain is allowed
to cool in the open air. Although advantageous for
examination, this open fire method of annealing has
several disadvantages, and is not to be recommended,
(i.) The iron, heated <in open air, is liable to oxida-
tion; (ii.) parts in contact with the fuel may be over-
heated and rendered brittle; (iii.) the various links in
the chain are not heated to a uniform temperature;
(iv.) the cooling takes place somewhat rapidly, and thus
reduces the annealing effect.

In the Docks Regulations the words “ annealing or
firing ” are used, and in some works firing is taken to

mean merely placing on a smith’s fire a pile of chains
covered with fuel, and turning on the air blast to raise
the temperature. As a rule this operation takes place
on Saturday, and the chains, after being heated, are
allowed to cool on the hearth until the following Monday.
This method is faulty, in so far as some links are over-
heated, while others are not raised to a temperature
sufficient to have any useful effect, and, therefore, the
chains cannot be considered as “ effectually softened,”
although this is difficult of proof.

Another method of annealing is used frequently where
wood is readily obtainable. The chains are either
placed on a grid supported above the ground, or hung
from a bar supported by the sides of a specially con-
structed pit, or by uprights. A wood pile is built over
the chains, oak wood being preferred, the chains are
heated by the wood fire and allowed to remain in
position until the ashes are cold. Satisfactory results
are claimed for this method of annealing, as wood is free
from sulphur and phosphorus, and does not affect the
metal injuriously; the temperature of a wood fire is
comparatively low, and the metal is not overheated and
rendered brittle. Chains are' also sometimes annealed by
heating them in a wood fire made on the hearth of an
ordinary plate or reverberatory furnace.

A rolled bar of iron is somewdiat harder on the exterior
than in the interior; this hardened skin is generally
retained after the bar has been converted into a chain,
and prevents, to some extent, wear of the links.
Annealing tends to make the surface softer and more
ductile; hence, an 'annealed chain is liable to wear more
rapidly. In addition tio the actual reduction in ultimate
strength, there is always a slight loss of material due to
oxidation, and the links- of a chain, after repeated
annealing, become appreciably reduced in. diameter, and
thus weakened. This loss may be obviated by “ close
annealing.” Some consider that annealing tends to
open the welds of the chain links at their edges, but
this view is not generally accepted. Opening of the
welds may possibly be due to subsequent testing of the
chain, and not to annealing.

The period between consecutive annealings of chains
and other appliances should depend on the time taken
to harden tlhe material by overstrain under ordinary
working conditions. A chain may be more overstrained
and become brittle sooner by a single severe shock than
by weeks of steady use. If possible, any overstrained
chain should be annealed at once, but this is seldom
practicable. It is, therefore, the practice of railway
companies and other large users to specify definite
periods (roughly based on the nature and amount of
work done by the chains) for annealing different classes
of chains. Those tin constant and severe use, such as
crane chains for loading or unloading coal at docks, are
often annealed once in every three months; for less
frequent and severe use, once in every six months. All
sling chains, and chains on power-driven lifting appli-
ances should be annealed once a year, whilst for chains
of hand cranes which are only used occasionally, the
period for annealing may be tWo or three years.

AMERICAN EXPERIENCE WITH
PERMISSIBLE EXPLOSIVES.

The beneficial effect of the use of low temperature
quick flame explosives in reducing the fatality rate in
bituminous coal mines, was explained by Mr. Van H.
Manning to the mining section of the National Council
for Industrial Safety, which met at Philadelphia.

The principal result of the work of the Bureau of
Mines has been in the development of the movement
for greater safety and better health conditions in the
mining, metallurgical, and allied industries of the United
States. It has received the hearty support of the mining
companies throughout the United States in all its efforts
to reduce the hazards of those industries. In conduct-
ing its campaign for the increase of safety in the mining
industries, the general plan of co-operation between the
National Government and other large agencies is :—(1)
That the National Government should conduct the
necessary general enquiries and investigations in rela-
tion to mine safety, and disseminate the information
thus obtained and the conclusions reached; (2) that each
State should enact needed legislation and make ample
provision for the proper inspection of mining operations
within its borders; (3) that the mine owners should
introduce improvements with a view to increasing safety
as rapidly as the practicability of such improvements is
demonstrated; and (4) that the miners and mine
managers should co-operate in drafting and enforcing
safety rules, regulations, and laws. The States, miners,
mine owners, and other agencies, such as mining and
engineering societies, are showing a commendable will-
ingness to co-operate with the National Government in
this safety work.

Among the principal investigations conducted by the
Bureau tending toward the reduction of coal mine acci-
dents are those relating to gas and dust explosions, the
use of explosives and electricity, and a study of safety
lamps. It has also done much work in the development
of mine rescue and first-aid apparatus, and has conducted
a compaign of education whereby these appliances may
be used most effectively. Thousands of miners are now
able to administer first-aid to their injured fellow work-
men. Suffering is reduced, and many lives saved.

When Congress first authorised the investigation of
the causes of mine explosions, it was not generally
believed that coal dust alone could spread an explosion
throughout a mine. Now that the explosibility of coal
dust has been demonstrated by the Bureau through work
in the laboratory, in the field, and in its-experimental
mine, the Bureau’s efforts are being directed toward the
devising of effective and practical methods of preventing
or arresting explosions. Through the development and

use of rock dust barriers and other devices, the intensity
of future coal mine explosions will most certainly be
decreased.

Permissible Explosives.

A systematic investigation has been made of the possi-
bility of coal mine explosions starting from improper use
of explosives or using improper explosives, or. from
electric sparks, miners’ lamps, mine fires, or other
agencies.

The Bureau has carried on a number of investigations
as to the nature of explosives used in mining operations,
with a view to changing the character of explosives so as
to meet the needs of the various branches of mining, and
especially to increasing safety in coal mines. Both the
wrong use of explosives and the use of an explosive not
suitable for certain classes of work have resulted in
coal mine disasters. The Bureau has brought about
what is little short of a revolution through the intro-
duction of new types of low temperature quick flame
powders, designated as “ permissible explosives,” in the
more dangerous coal mines of the country.

Fatalities Decrease.

In the bituminous coal mines of the United States
the fatality rate from explosives per 10,000 men
employed has been reduced from 3*39 in 1903, to 0’96
in 1914, largely as a result of the use of permissible
explosives.

Through the activity of the Bureau in calling atten-
tion to dangers in the use of electrical machinery in
mines, manufacturers have devised safer types of
apparatus, and States have enacted stricter laws govern-
ing electric installations.

Safety Lamps.

An investigation of electric lamps for miners has
resulted in greatly improving the types now offered'for
sale. In regard to safety lamps other than electric,
tests have been made to ascertain the comparative
merits of different types of safety lamps, including
their usefulness in furnishing light to miners, their
relative safety, and their value in indicating the pre-
sence of explosive gas.

FORMATION OF COAL AND PEAT.

Charles A. Davis, fuel technologist at the Bureau of
Mines, describes as follows the manner in which peat,
lignite, coal, and graphite are formed :—Peat is incipient
coal. It is made up of the more or less thoroughly
decomposed and carbonised remains of plants accumu-
lated under conditions that have prevented their com-
plete transformation into gaseous and mineral matter.
In the course of their growth, plants segregate carbon
dioxide from the gases of the atmosphere, and, by the
aid of sunlight, decompose it and water in their green
tissues and re-combine the elements into complicated
organic compounds, in which carbon is the characterising
element. If the compounds formed in this way by
practically all green plants decay in the air, they are
slowly changed back to gases again, chiefly by the
activities of plants and animals of low orders, the bio-
chemical agents of decomposition. If, however, the air
is excluded from accumulations of plant material,
chemical and physical changes of quite a different
character take place—and much more slowly than when
air is present—by which the vegetable matter loses
only a part of its constituents. In the course of such
changes and losses, two gases—hydrogen and oxygen,
the chemical elements that form water—disappear more
quickly than carbon, the third important chemical
element, which, in combination with them, forms cellu-
lose and lignin, the compounds of which most plant
tissues and organs are composed. The carbon is concen-
trated as such changes continue, and the original plant
material becomes more and more nearly pure carbon.
Peat, lignite, coal, anthracite, and graphite, a form of
carbon, are successive stages in this process of carbonisa-
tion as it is represented in nature. Similar changes are
made in wood or other plant structures when they are
heated in closed vessels, the residue left after heating
being charcoal, also a form of nearly pure carbon.

- Partnerships Dissolved.—The London Gazette announces
the dissolution of the following partnerships :—Martha A.
Dunlop, H. G. Lear, and Fred H. Tuxworth (being the
executors of Herbert William Dunlop, late of “Maison-
nette,” Earley), and Thomas T. English, coal merchants;
A. Williams and J. G. Luff, colliery agents, ship brokers
and coal exporters, at Queen’s-buildings, Swansea, under the
style of Williams, Luff and Company; A. Nicklin and C. E.
Smith, coal dealers, at Fenton, Stafford, under the style of
Nicklin and Smith; A. E. Arthurton and G. T. West, carry-
ing on business as mineral merchants at Bakewell, Derby-
shire, under the style of Arthurton, West and Company; J.
Bilbie, J. S. Wylde, and H. G. Hale, carrying on business
as engineers at 106, Queen Victoria-street, London, E.C., and
Deverell-street, Great Dover-street, London, S.E., under the
style of Bilbie, Hobson and Companv, so far as concerns
H. G. Hale.

Lectures on Coal.—At the University of London, University
College, Department of Botany, on Tuesdays at 5 p.m.,
beginning January 18, Dr. Marie Stopes will give a course
of public lectures on “ Coal.” The lectures are intended for
advanced students in botany and geology and others interested
in mining, etc. The following subjects will be dealt with :
The microscopic structure of coal; spore coals ; so-called “algal
coals ” ; resin in coal, its presence in palaeozoic coals, and the
reasons for its apparent absence; the relation between the
plants forming the coal, and its ultimate character; cannel,
bituminous, anthracite, and other coals; coal dust; the soils
and surfaces on which coal accumulated; “ drift ” and in situ
coals : earth movements and their effects on the composition,
and distribution of coal; the inter-relation of palaeogeography
and the conditions of coal deposition ; true coals of various
countries from the tertiary to the palaeozoic; unfinished coals,
neats, brown coals, etc.; coal resources of the world. The
lectures are open to the public without fee or ticket.